The present invention relates to a transfer ring for a tire assembling machine.
In the tire industry, it is current practice to produce a tire carcass including essentially the entire carcass with the exception of the outer annular reinforcements and the tread which form a belt which is to be positioned precisely on said carcass. This belt is produced separately; in fact, due to its geometry and its positioning on the outer annular surface of the carcass it is preferable to grasp the belt on its outer annular surface, in order to transfer it. For this, there is generally used a transfer ring provided with means for grasping the outer circumference of the belt, this transfer ring being able also to make it possible to displace then the complete tire produced.
This transfer operation is of great importance in the manufacture of the tire. In fact, the tires must be balanced, which means a precise positioning of the components of the tire, on the one hand, uniformly on the circumference of the tire and, on the other hand, symmetrically with respect to the radial median plane of the tire. Furthermore, the slight rigidity of the ring formed by the belt in raw state requires careful transfer in order not to run the risk of deforming it when it is grasped.
EP-A 0 700 774 describes a transfer ring for a tire belt formed of two coaxial annular disks, one of which, the inner one, is stationary, while the other, the outer, is movable in rotation around the axis of the ring. This transfer ring has grippers connected respectively to each of the disks by a rod so that the rotation of the outer disk results in a radial displacement of the grippers in order grasp the belt, said rotation being effected by means of an actuator located radially to the outside of the outer disk.
Such a transfer ring makes it possible to grasp belts of different diameters. However, this characteristic is accompanied by a very large radial size. Now, it is current practice that transfer rings, upon the placing of the belt, must be positioned between the support bearing the carcass and a roller device used in order to effect good application of the belt onto the carcass. This considerably limits the outer radial space permissible for the transfer ring.
U.S. Pat. No. 4,667,574 describes a transfer ring for a tire belt comprising grippers which are displaceable radially in order to grasp the belt, and are driven respectively by a pneumatic actuator. By a piston housed in the body of the gripper in question an actuator controls the radial displacement of said gripper up to a piston-stop position corresponding to the definition of the diameter of the belt to be grasped.
Such a transfer ring can therefore only be one-dimensional. Furthermore, the actuators used for this ring exert a relatively substantial pressure on the belt upon its transfer so that there is a danger of deforming said belt.
Furthermore, in the two documents mentioned the transfer rings disclosed require a very precise adjustment of coaxiality with respect to the form which initially bears the belt and to the assembly support on which it is to be placed. In fact, in order to permit a proper grasping of the belt, the diameter defined by the position of the grippers must be perfectly centered on said belt.
Publication GB-A-2 092 100 is distinguished from the publication U.S. Pat. No. 4,667,574 previously cited by the fact that the displacement of the grippers is stopped by a device for blocking the piston rod in a direction perpendicular to the radial displacement of said rod. This device makes an independent displacement of each gripper possible, but it requires not only actuators with a rod which take up a lot of space but also the presence of blocking devices (14) which further increase the space taken up radially. The multi-dimensional character of such a transfer ring is therefore limited to very slight differences in diameter. Furthermore, as indicated in connection with the device disclosed in U.S. Pat. No. 4,667,574, the operating pressure of the type of actuator used for this ring is problematical.